Think about how slow that Rossi twist is. 1 twist in 30 inches. The marlin .357 rifle is 1 in 16. My 9mm M&P has a 10 inch twist.
With using the Lee 125-rf in the fast twist 9, my range scrap alloy begins to strip the riflings around 1050 fps. This leaves leading along the rifling paths. I can take the same 125-rf out of soft range scrap well over 2000 fps in the slow twist Rossi with no leading.
Think about this - to torque the rifling paths as hard the 10 inch twist m&p at 1000 fps, the 30 inch twist Rossi would have to be going 3000 fps - AND the Rossi has 4-5 times the barrel to gently accelerate the bullet. The 158-rf shoots within 3 MOA with softer-than-wheelweights range scrap at 16-17 grains of Lil gun (1.09 or 1.18 CC volume) in my rifle. I did have to fire lap out some machining marks near the muzzle but after 25 or so firelapping shots I can shoot soft lead really fast with this (basically) round ball twist.
The down side is that the Marlin can shoot 220 grain sub sonic, where the Rossi only likes WFN 158s subsonic, not even the longer 158 SWC. The upside to the slow twist is that gas checks aren't a part of your budget. I would love to hear what LArry Gibson has to say about his RPM theory and the DRAMATIC differences in twist between 10" twist 9m and 30" twist 357 rifle and what that means for accuracy and bullet alloy.